Board Thread:General Discussion/@comment-26222858-20150917141812/@comment-26222858-20151002135649

His power awakened in DMC3, which is why he switched into DT at that moment, and in DMC4, he was already matured :D So it's not entirely debunked, as Dante never lets go of his sword after receiving his DT in 3.

In DMC1, he didn't use Rebellion, he used Force Edge which was stronger than Rebellion. He didn't need DT until later, when bosses and such were introduced, which is why the door of judgement impales Alastor into him and bestows him with the power of Alastor, through the Devil Arm.